The field of the invention is systems and methods for creating images using an ionizing radiation source. More particularly, the invention relates to systems and methods for creating medical images using a polychromatic source with single energy spectrum to create multi-energy imaging data sets and corresponding images.
Dual-energy computed tomography (CT) imaging was proposed in 1970s and, since then, has experienced several up-and-downs in practical implementation and also applications. In recent five years, dual-energy CT has been commercialized by several companies to provide quantitative discrimination in materials such as iodine and calcium and focused on clinical applications, such as the differentiations between different kinds of renal stones. While the practical uses of dual-energy CT imaging has been established, there are a variety of lingering challenges that have impeded the wide-spread adoption of dual-energy CT imaging in clinics.
First, the commercially-available dual-energy CT systems require specialized hardware, such as data acquisition systems. For example, turning to FIGS. 1 and 2, a traditional dual-energy, CT system is illustrated, such as is commercially available. In particular, a dual-energy CT imaging system 10 includes a gantry 12 having a one or more x-ray sources 13 (13′) that project a fan beam or cone beam of x-rays 14 (14′) toward a detector array 16 (16′) on the opposite side of the gantry 12. As illustrated, there may be a single source 13 or two or more source 13′. That is, some commercially-available, dual-energy systems employ a single source 13 that is switched between high and low energies and other commercially-available, dual-energy systems employ two dedicated sources 13, 13′ that are used to generate the high and low energies. That is, to enable dual-energy CT imaging, one either require two tube two detector technique, or one has to have special x-ray generator, tube, and also detector to enable fast kV switching acquisition technique, or a special sandwich detector or photon counting detector to enable energy resolving x-ray detections. The detector array 16 (16′) is formed by a number of detector elements 18 that together sense the projected x-rays that pass through a medical patient 15. Each detector element 18 (18′) produces an electrical signal in response to receiving photon or bunches of photons.
During a scan to acquire x-ray projection data, the gantry 12 and the components mounted thereon rotate about a center of rotation 19 located within the patient 15 to acquire attenuation data. The rotation of the gantry and the operation of the x-ray source(s) 13 (13′) are governed by a control mechanism 20 of the CT system. The control mechanism 20 includes an x-ray controller 22 that provides power and timing signals to the x-ray source(s) 13 (13′) and a gantry motor controller 23 that controls the rotational speed and position of the gantry 12. A data acquisition system (DAS) 24 in the control mechanism 20 samples analog data from detector elements 18 and converts the data to digital signals for subsequent processing. An image reconstructor 25, receives sampled and digitized x-ray data from the DAS 24 and performs high speed image reconstruction. The reconstructed image is applied as an input to a computer 26 which stores the image in a mass storage device 28.
The computer 26 also receives commands and scanning parameters from an operator via a console 30 that has a keyboard. An associated display 32 allows the operator to observe the reconstructed image and other data from the computer 26. The operator supplied commands and parameters are used by the computer 26 to provide control signals and information to the DAS 24, the x-ray controller 22, and the gantry motor controller 23. In addition, the computer 26 operates a table motor controller 34 that controls a motorized table 36 to position the patient 15 in the gantry 12.
Whether employing two, dedicated sources 13, 13′ or switching operation of a single source 13 between two tube potentials, these dual- or multi-energy imaging systems are generally of higher cost and complexity than traditional imaging systems due to the need for specialized hardware and software, such as additional sources 13′, detector arrays 16′, and communications and software for processing feedback from different energy levels from individual detector elements 18, 18′.
Second, regardless of the hardware, maintenance, and operational cost and complexities, traditional dual- or multi-energy CT imaging systems subject the patient 15 to a higher dose of ionizing radiation than a non-dual-energy CT imaging process. That is, a dose of high-energy radiation is delivered to the patient 15 and a does of low-energy radiation is delivered to the patient 15.
Therefore, it would be desirable to provide systems and methods for performing dual- or multi-energy imaging without the need for two separable x-ray energy spectra and also highly-specialized, expensive, and complex hardware and/or delivering two doses of radiation tot the patient.